Providing forward secrecy in a terminating SSL/TLS connection proxy using ephemeral Diffie-Hellman key exchange

Abstract

An infrastructure delivery platform provides a proxy service as an enhancement to the TLS/SSL protocol to off-load to an external server the generation of a digital signature, the digital signature being generated using a private key that would otherwise have to be maintained on a terminating server. Using this service, instead of digitally signing (using the private key) “locally,” the terminating server proxies given public portions of ephemeral key exchange material to the external server and receives, in response, a signature validating the terminating server is authorized to continue with the key exchange. In this manner, a private key used to generate the digital signature (or, more generally, to facilitate the key exchange) does not need to be stored in association with the terminating server. Rather, that private key is stored only at the external server, and there is no requirement for the pre-master secret to travel (on the wire).

What is claimed is as follows: 
     
       1. A method, comprising:
 configuring a trusted machine into a secure physical environment, the secure physical environment being managed by a service provider; 
 configuring an untrusted machine to selectively proxy key exchange material to the trusted machine; 
 during a Transport Layer Security (TLS) connection handshake request received from a client at the untrusted machine, the untrusted machine configured to:
 provide to the client a public certificate for a domain, the public certificate having a public key of an asymmetric key pair, a private key of the asymmetric key pair being held in the secure physical environment of the trusted machine and therefore being inaccessible to the untrusted machine, the private key configured to digitally sign information associated with an elliptic curve-based Diffie-Hellman ephemeral key exchange; 
 transmit to the trusted machine data associated with the elliptic curve-based Diffie-Hellman ephemeral key exchange, the data including at least a server public Diffie-Hellman value; 
 receive from the trusted machine a digital signature, the digital signature having been generated at the trusted machine by applying the private key to the data; 
 transmit to the client the digital signature, together with the data; 
 receive from the client a client public Diffie-Hellman value, the client public Diffie-Hellman value having been generated by the client using a client private Diffie-Hellman value and at least some of the data; and 
 generate a pre-master secret based at least in part on the client public Diffie-Hellman value. 
 
 
     
     
       2. The method as described in  claim 1  wherein the data also includes public parameters of the elliptic curve-based Diffie-Hellman ephemeral key exchange. 
     
     
       3. The method as described in  claim 2  wherein the public parameters include a prime modulus, and a generator. 
     
     
       4. The method as described in  claim 2  wherein the data also includes one of: a client nonce, and a server nonce. 
     
     
       5. The method as described in  claim 2  wherein the public parameters of the elliptic curve-based Diffie-Hellman ephemeral key exchange are generated during the handshake request. 
     
     
       6. The method as described in  claim 2  wherein the public parameters of the elliptic curve-based Diffie-Hellman ephemeral key exchange are generated in advance of the handshake request. 
     
     
       7. The method as described in  claim 2  wherein the public parameters of the elliptic curve-based Diffie-Hellman ephemeral key exchange are used only for the handshake request. 
     
     
       8. The method as described in  claim 2  wherein the public parameters of the elliptic curve-based Diffie-Hellman ephemeral key exchange are used during the handshake request and at least one other handshake request. 
     
     
       9. The method as described in  claim 2  wherein the public parameters are selected from a set of public parameters generated in batch at the untrusted machine. 
     
     
       10. The method as described in  claim 1  wherein the elliptic curve-based Diffie-Hellman ephemeral key exchange utilizes an RSA cryptographic algorithm.